phy: rockchip: samsung-hdptx: Optimize internal rate handling

Drop the rate parameter from a bunch of internal helpers and, instead,
make better use of the newly introduced ->hdmi_cfg.tmds_char_rate driver
data.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250318-phy-sam-hdptx-bpc-v6-13-8cb1678e7663@collabora.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>